Daytime light exposure dynamically enhances brain responses

Exposure to light is known to enhance both alertness and performance in humans, but little is understood regarding the neurological basis for these effects, especially those associated with daytime light exposure. Now, by exposing subjects to light and imaging their brains while they subsequently perform a cognitive test, researchers have begun to identify brain regions involved in the effects on brain function of daytime light exposure. The findings are reported by Gilles Vandewalle and Pierre Maquet of the University of Liège, Derk-Jan Dijk of the University of Surrey, and additional colleagues and appear in the August 22nd issue of the journal Current Biology, published by Cell Press.

Our brain does not use light only to form images of the world. Ambient light levels are detected by our nervous system and, without forming any image, profoundly influence our brain function and various aspects of our physiology, including circadian rhythms, hormone release, and heart rate. These responses are induced by a special non-image-forming (NIF) brain system, which researchers have begun to characterize in animal models. In human studies, much work has focused on the effects of nighttime light exposure, but little is known about daytime responses to light. Especially mysterious are the neural correlates of these responses, and their temporal dynamics. Such issues are of significant interest given that daytime sleepiness is a major source of complaint in modern society and has considerable socio-economic implications.

In the present study, the researchers showed that a brief (21-minute) morning exposure to a bright white light increases alertness and significantly boosts the brain's responses to an experimental test that requires attention only to sound. In a parallel neuroimaging analysis, this boost in alertness was found to correlate with responses in various areas of the brain, including regions of the cortex known to support performance on the auditory test. The regional brain changes were found to be highly dynamic, dissipating within a few minutes. These new findings therefore show that light exposure, even during the day, can quickly modulate regional brain function in areas involved in alertness and non-visual cognitive processes.